Abstract. The supercooled liquid fraction (SLF) in mixed-phase clouds (MPCs) is an essential variable of cloud microphysical processes and climate sensitivity. However, the SLF is currently calculated in spaceborne remote sensing only as the cloud phase–frequency ratio of adjacent pixels, which results in a loss of the original resolution in observations of cloud liquid or ice content within MPCs. Here, we present a novel method for retrieving the SLF in MPCs based on the differences in radiative properties of supercooled liquid droplets and ice particles at visible (VIS) and shortwave infrared (SWI) channels of the geostationary Himawari-8. Liquid and ice water paths are inferred by assuming that clouds are composed of only liquid or ice, with the real cloud water path (CWP) expressed as a combination of these two water paths (SLF and 1-SLF as coefficients), and the SLF is determined by referring to the CWP from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). The statistically relatively small cloud phase spatial inhomogeneity at a Himawari-8 pixel level indicates an optimal scene for cloud retrieval. The SLF results are comparable to global SLF distributions observed by active instruments, particularly for single-layered cloud systems. While accessing the method's feasibility, SLF averages are estimated between 74 % and 78 % in Southern Ocean (SO) stratocumulus across seasons, contrasting with a range of 29 % to 32 % in northeastern Asia. The former exhibits a minimum SLF around midday in summer and a maximum in winter, while the latter trend differs. This novel algorithm will be valuable for research to track the evolution of MPCs and constrain the related climate impact.

中文翻译：

---

技术说明：从 Himawari-8 观测中反演混合相云中的过冷液体部分


摘要。混合相云（MPC）中的过冷液体分数（SLF）是云微物理过程和气候敏感性的重要变量。然而，目前星载遥感中的SLF仅计算为相邻像元的云相频比，这导致MPC内云液体或冰含量观测中原始分辨率的损失。在这里，我们提出了一种基于对地静止 Himawari-8 可见光 (VIS) 和短波红外 (SWI) 通道的过冷液滴和冰粒辐射特性差异来反演 MPC 中 SLF 的新方法。液体和冰水路径是通过假设云仅由液体或冰组成来推断的，真实云水路径（CWP）表示为这两种水路径的组合（SLF和1-SLF作为系数），并且SLF是参考云气溶胶激光雷达和红外探路者卫星观测（CALIPSO）的CWP确定的。 Himawari-8 像素级别的统计上相对较小的云相空间不均匀性表明云检索的最佳场景。 SLF 结果与有源仪器观察到的全球 SLF 分布相当，特别是对于单层云系统。在评估该方法的可行性时，南大洋 (SO) 层积云各个季节的 SLF 平均值估计在 74% 到 78% 之间，而东北亚的范围为 29% 到 32%。前者在夏季中午左右表现出最低 SLF，在冬季表现出最高，而后者的趋势则有所不同。这种新颖的算法对于追踪 MPC 的演化和限制相关的气候影响的研究非常有价值。